Generally local or regional health units issue heat alerts when temperatures and/or humidex values are expected to reach levels that place public health at risk. They often cite infants, children, the elderly and people with heart and/or respiratory problems as those at particular risk of developing a heat-related illness.
 
Heat and humidity can also be a significant hazard to workers throughout the year but especially in summer. Those at risk are employed in the construction industry, landscaping, farming, public works and other outdoor jobs. Working in hot and/or humid indoor environments such as bakeries, commercial kitchens, laundries, factories and warehouses can also place workers in harm’s way.  
 
Affected workers may experience rashes, cramps, weakness, dizziness and fainting. If not promptly treated, these symptoms can progress to heat exhaustion, heat stroke and even death.
 
In addition to the risk posed by heat and humidity, outdoor workers can also be exposed to the sun's ultraviolet (UV) radiation. According to CAREX Canada nearly one in 10 Canadian workers are exposed to UV radiation at work. Prolonged exposure can cause acute and chronic damage to the eyes and skin including skin cancer — the most common cause of cancer.
 
Ontario employers have a legal duty to take every precaution reasonable in the circumstances to protect workers [section 25(2)(h), Occupational Health & Safety Act (the Act)].
 
Precautions can include reducing the physical demands of a job, adding rest breaks or, when needed, stopping work altogether. Precautions should also include the development and implementation of a heat stress/summer hazards prevention policy and procedures. This should be developed in consultation with the joint health and safety committee or worker representative and include both a worker and supervisor training component. Beyond general awareness and prevention, this training should focus on the signs and symptoms of heat stress and what to do when they are observed or experienced. 
 
Also relating to the Act's "reasonable precaution" duty, Ministry of Labour (MOL) inspectors rely on threshold limit values (TLVs) for heat stress published by the American Conference of Governmental Industrial Hygienists (ACGIH).
 
The Occupational Health Clinics for Ontario Workers (OHCOW) offers resources to help focus workplace efforts on prevention, including a sample Humidex/Heat Stress Response Plan based on the ACGIH TLVs. OHCOW also offers a Humidex-Based Heat Stress Calculator on their web site (see link below).
 
For our part, the Workers Health & Safety Centre (WHSC) offers a detailed Heat Stress training program focusing on general awareness along with workplace-specific prevention strategies to eliminate exposure or reduce the risk to worker health. Also available is the WHSC’s Heat Stress: cool solutions fact sheet.  
 
Want to know more about the WHSC Heat Stress Training — call toll free 1-888-869-7950 and ask to speak to a training service representative?
 
Want to access workplace heat stress assessment tools developed by OHCOW?

• OHCOW Humidex Heat Stress Response Plan
• OHCOW Humidex Calculator
• OHCOW publication Hazards of Working in the Sun